1. Field of the Invention
The present invention relates to couplings for joining tubes that carry fluid and more particularly to the field of quick connect couplings of this type.
2. Description of the Prior Art
The quick connect tubular coupling described in U.S. Pat. No. 4,055,359 permits a fluid-tight connection to be made between the tubes by hand in a short time. In making this connection the operator merely applies axial force to one of the tubes and a resistance force in the opposite direction to the other tube. This action causes a garter spring to expand around the flanged end of one of the tubes and into a locking position within a cage member. It is necessary in joints of this type that carry pressurized fluid that a positive hydraulic seal be an integral part of the joint. To this end the coupling described in the patent includes at least one O-ring received in a groove formed in one tube end. The O-ring is compressed when the second tube is inserted over the first tube with an interference fit.
The difficulty with this coupling arises by reason of the frictional contact between the rubber O-rings and the metal tube end. The O-rings must be compressed in order to produce the requisite seal but this compression produces a force between the members. Consequently, a frictional force is developed on the mating surfaces whose magnitude is generally sufficient to hold the tube ends together even though the garter spring has not been expanded over the flared end of the second tube and into its locking position. Often in the assembly process it has been discovered that the coupling gives the appearance of a properly connected coupling because the frictional forces hold the tube ends in substantially the same relative positions as they would have if the connection were properly made. If the garter spring has not been forced into its locking position, the tube ends retained only by the frictional force are readily separated when the fluid circuit is pressurized under operating conditions in normal use. Loss of the fluid carried in the system requires its replacement and often return of the system to the factory because of an apparently faulty coupling.
It is preferred that some visible means clearly observable by the operator making the connection be available so that a faulty connection can be avoided. Furthermore, the visible indication that the joint has been properly assembled should continue to exist after the connection is made so that upon inspection at a later point in the manufacturing cycle there is no need for occasional disassembly of the coupling to ascertain whether the connection has been properly made.